It has been known in the prior art to use NDIR technology for gas analyzers due to the performance of such analyzers to be highly specific, sensitive and reliable. These gas analyzers use an optical waveguide or chamber containing the gas to be measured positioned between a light source and a detector. The light emitted from the light source travels through the chamber, and the gas contained therein, until it reaches the detector element for indicating gas concentrate levels. The major drawback of the past NDIR gas measurement devices has been their expense and complexity.
One attempt to overcome these difficulties with NDIR devices has been to use a diffusion-type gas chamber. U.S. Pat. No. 4,709,150 to Burough et al. issued Nov. 24, 1987 discloses such a device using a porous material tube for the gas sample chamber. Such a chamber allows the gas to be measured to flow through the porous walls. Another example as disclosed in U.S. Pat. No. 5,163,332 to Wong issued Nov. 17, 1992 uses a gas chamber with filtered apertures contained therein, and a highly specularly reflective inner surface. The use of this diffusion-type chamber eliminates the need for expensive optics, mechanical choppers and a gas supply and discharge means for adding to and taking away sample gas from the chamber.
These analyzers with the diffusion-type gas chamber, however, still suffer from generally high cost and complexity as well as reliability difficulties such as drift problems caused by variations in light source intensity and variations in environmental conditions such as ambient temperature.